1. Field of the Invention
The present invention relates to an OLED display device, and more particularly, to an OLED display device with high output impedance.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a circuit diagram illustrating a conventional OLED display device 100. The OLED display device 100 comprises a current source 110 and an OLED equivalent module 120. The current source 110 comprises a voltage source VH, a controller 111, and a p-type transistor Q1. The OLED equivalent module 120 comprises 2 resistors R1 and R2, an OLED D1, and an equivalent capacitor C1. The voltage source VH biases the p-type transistor Q1 at the saturation region. The current source 110 transmits controlling voltage V1 to the gate of the p-type transistor Q1 to control the current I1 by the controller 111. Theoretically, the output resistance of the current source should be infinite, and thus, no matter what the load coupled to the current source is, stability and output abilities of the current source are not affected. In fact, the conventional current source 110 has an equivalent output resistor having a resistance of Rd. Thus, if the OLED equivalent module 120 overloads the current source 110, that is, the equivalent load resistor of the OLED equivalent module 120 is not ignored compared with the resistor Rd, the current I1 is affected and the size of the current I1 is changed from the ideal status. Thus, the lumen is not even everywhere on the OLED display device.